Electro-hydraulic servo actuators



July 22, 1958 T. H. CARSON ELECTRO-HYDRAULIC SERVO ACTUATORS Filed Aug. 29, 1955 IN V EN TOR. T. C/msoN ATTORNEYS United States Patent 2,844,158 ELECTRO-HYDRAULIC SERVO ACTUATORS Thomas Howard Carson, Seattle, Wash, assignor to Ex-Cell-O Corporation, Detroit, Mich. Application August 29, 1955, Serial No. 530,944 7 Claims. (Cl. 137-82) This invention relates to an electro-hydro servo actuator of the general type in which a nozzle supplied from a source of high pressure fluid and an electric motor are utilized to convert a" low-level electrical signal into a proportional hydraulic actuating force.

By Way of background, it has been well known in the servo art to have the armature of a torque motor arranged as a flapper, selectively restricting flow from a nozzle to thereby vary the nozzle back pressure, this pressure being used to actuate a valve spool or some other part of the servo proper. Furthermore, it has been common practice, as shown in U. S. Patent No. 2,625,136, issued Jan. 13, 1953, to subject all of the parts of the torque motor to the return flow of fluid after it has discharged from the nozzle against the armature. The fluid, though normally filtered continuously, is never completely free of minute foreign particles as it repeatedly passes the torque motor and gradually in many cases so many of these particles adhere by magnetic attractionto the motor parts that effective operation of the torque motor is seriously impaired.

The present invention has as its principal object the providing of an improved electro-hydraulic actuator of simple construction wherein the torque motor is substantially bypassed by the return flow of fluid from the nozzle without incorporating structure causing loss of sensitivity.

With yet additional objects and advantages in View which, with the foregoing, will appear and be understood in the course of the following description. and claims, the invention consists in the novel construction and in the adaptation and combination of parts hereinafter described and claimed.

In the accompanying drawings:

Figure 1 is a front longitudinal elevational view of a servo valve incorporating my actuator and with part of the valve being broken away to show my actuator in vertical section.

Fig. 2 is a fragmentary perspective view partly in section and to an enlarged scale illustrating the operative parts between the armature and the nozzle; and

Fig. 3 is a transverse vertical sectional view taken along line 3-3 of Fig. 1.

For purposes of example I have illustrated my actuator mounted in'the head end of the housing 7 of a servo. This housing has a removable hollow cap 8 providing a chamber9 for a torque motor 10. The motors armature is denoted 1'1 and is extended at one end to have, in

a manner to be later explained, operative association with a nozzle 12. Extending longitudinally of the housing 7 from the chamber 9 are bores providing a return passage 13 and a supply passage 14. The bore for the latter is counterbored commencing at 15 to provide a shoulder against which is seated a cylindrical diaphragm retainer 16. This retainer is closed at its forward end by an elastic circular diaphragm 17 which is fitted by its rim in an annular groove formed in the retainer. A plurality of radially extending ports 18 radiate from the interior of the retainer to a circumferential exterior groove 20 which communicates by a cross passage 21 with the discharge passage 13. Rearwardly of the intersection of the passages 21 and 13 the latter is counterbored thereby forming a seat 22 for an insert 23. This Patented July 22, 1958 insert is externally sealed by an O-ring 24 and provides a central return orifice 25 from whence the passage 13 feeds to a suitable return line leading from the housing 8.

Seated against the rear end of the diaphragm retainer 16 is a centrally bored nozzlemember 26. This member has the nozzle 12 as a reduced head projecting into the retainer 16 and tapering at its nose to a restricted nozzle opening. An O-ring 27 seals off the nozzle member externally. The nozzle 12 is spaced from the surrounding side wall of the retainer 16 to provide a chamber 28 for fluid discharging from the nozzle. This fluid normallyis fed to the supply passage via a supply line leading from a source of high pressure .fluid remote to the housing 7. A flow restrictor is desirably placed in the supply passage in advance of the nozzle and between this restrictor and the nozzle is located a take-oil? leading'to aslide valve or any other part of the servo to be actuated by the nozzle back pressure.

A disc-like flow restricting member 29ris spaced by a small gap from the nozzle tip. It will be noted that this member 29 is circumferentially grooved so that the diaphragm, which has a central opening smaller in diameter than that of the restricting member 29, can make a snap fit therewith. Thus the retainer 16, diaphragm 17 and flow restricting member 29 may be considered as a diaphragm assembly.

A stem 30 extends forwardly from the diaphragm assembly as an integral prolongation of the restricting member and has a pointed head 31. This head engages a beveled seat 32 provided in the foot of a male adjusting screw 33. Theother end of the screw 33 is formed with an Allen head and is threaded through the extended end portion of the armature 11. A spiral tension spring 34 encircles the stem 30 and has its root end 35 anchored by passing laterally through a hole in the stem. As best seen in Fig. 2, the forward end of the spring has a few of its coils interfitting with threadsof the screw 33 so that the loading of the spring keeps the pointed head 31 seated.

In the torque motor 10, the armature 11 is pivoted by means of a hinge 36 mounted midway between the air gaps of two opposed pairs of poles 37, 38. These are supported by respective end plates 39, 40 between which a permanent magnet 41 is clamped. The two coils of the motor are denoted 42, 43 and arewound on respective spools 44, 45 encircling the armature. Beneath the head end plate 39,-the spools are separated by a length 46 of O-ring and diametrically opposite from the latter the inner opposed faces of the spools are modified to accommodate the hinge'36. The leads for the coils feed through the housing from a jack 47 mounted there- Application of a difierential current to the coils 42, 43 causes magnetization of the armature 11 and as a result one end of the armature is polarized north and the other south depending on the direction of the differential current. The armature will therefore be attracted toward two diagonally opposite of the poles 37, 38 and repelled by the other two poles. These forces of attraction and repulsion result in a rotation of the armature about its hinge 36 and a deflection of the armature in the vicinity of the adjusting screw 33. This deflection in turn is transferred to the flow restricting member 29 via the screw 33 and the stem 30, the diaphragm 17 yielding accordingly to prevent flow of fluid past the member 29 'without interferring with the sensitivity of operation, With this arrangement the magnitude of the.

thereof. forces urging deflection of the flow restricting member 29 is proportional to the magnitude of the differential current input signal to the coils 42, 43 and the direction of motion of such member into a more or less restricting position of the nozzle 12 is determined by which of the coils has the larger current. The adjusting screw 33 is utilized to set the size of gap between the nozzle 12 and the flow restricting member 29, and hence to set the nozzle back pressure, when the current differential between the coils 42, 43 is zero and the armature 11 is centered between the pairs of poles 37, 38,

Tracing the flow of fluid discharging from the nozzle against the flow restricting member 29, and remembering that the chamber 28 is isolated from direct communication with the motor chamber 9 by the diaphragm 17, the discharging fluid passes from the chamber 28 through the radial ports 18 to the annular space 20. From the latter the fluid travels into the cross passage 21 and then enters the return passage 13. The latter communicates directly with the motor chamber 9 and this is done so that there will be a static pressure balance on both sides ofthe diaphragm 17. However, after the motor chamber is once full of fluid there is very little tendency for fluid entering the return passage 13 from the cross passage 21 to circulate into. the motor chamber since its natural current is out through the return orifice 25 and thence ultimately to the return line running from the housing. Thus it can be seen that the torque motor is not subjected to a continual flow of fluid through its parts, and hence is not likely to have a build up of any magnetically attractable particles which may be suspended in the circulating fluid as it discharges from the nozzle.

The advantages of the invention, it is thought, will have been clearly understood from the foregoing detailed description of the illustrated preferred embodiment. Minor changes will suggest themselves and may be resorted to without departing from the spirit of the invention, wherefore it is my intention that no limitations be implied and that the hereto annexed claims be given a scope fully commensurate with the broadest interpretation to which the employed language admits.

What I claim is:

1. In an electro-hydraulic actuator, a housing formed with a motor chamber and a discharge chamber, a diaphragm mounted between said chambers, a flow restricting member carried by said diaphragm, a nozzle having a supply of high pressure fluid thereto and arranged to discharge into said discharge chamber in restricted relation to said flow restricting member, means for balancing the static pressures in said chambers, an electro-magnetic motor mounted in said motor chamber and having an armature forced towardand away from said diaphragm in response to electric input signals applied to said motor, an adjustment screw threaded into said armature, a stem extending between said screw and flow restricting member for moving the latter in response to movements of said armature thereby obtaining various nozzle back pressures as actuator output signals determined by said electric input signals.

2. In an electro-hydraulic actuator, an elastic diaphragm ,with .a center opening, a stem having a circumferentially grooved head inserted through said center opening with the rim of the latter fitting into the circumferential groove in said head, the other end of said stem being pointed, an armature, an adjusting screw threaded by one of its ends into said armature and presenting a beveled concave seat at its other end for receiving said pointed end of the stem, and a tensioned spiral spring locked at one of its ends to said stem and having its other end gripping said screw for urging the pointed end of the stem into said seat.

3. In an electro-hydraulic actuator, 21 housing formed with a motor chamber and a discharge chamber, a diaphragm assembly mounted between said chambers and including a nozzle flow restrictor, a nozzle arranged to discharge into said discharge chamber against said flow restrictor, means for balancing the static pressures in said chambers, electric motor means mounted in said motor chamber and operatively connected with said flow I4 l r restrictor for restricting flow from said nozzle in response to electric input signals applied to said motor means thereby obtaining respective nozzle back pressures as actuating output signals.

4. In an electro-hydraulic actuator, a housing formed with a motor chamber and a discharge chamber, a nozzle arranged to discharge into said discharge chamber, a diaphragm assembly mounted between said chambers and including a flow restrictor for said nozzle, means for balancing the static pressures in said chambers, electromagnetic motor means mounted in said motor chamber for selectively applying various input forces in response to electric input signals, and means for transferring said input forces to said flow restrictor for respectively restricting the flow from said nozzle thereby obtaining various nozzle back pressures as actuator output signals determined by said electric input signals.

5. In an electro hydraulic actuator, a housing formed with a motor chamber and a discharge chamber, a diaphragm mounted between said chambers, a flow restricter, a nozzle having a supply of high pressure fluid thereto and arranged to discharge into said discharge chamber against said flow restrictor, means for balancing the static pressures in said chambers, an electro-magnetic motor mounted in said motor chamber and having an armature arranged to move toward and away from said nozzle by forces acting on said armature in response to electric input signals applied to said motor, and means operatively connected to said armature and diaphragm for transferring said forces through said diaphragm to said flow restrictor for respectively restricting the flow from said nozzle thereby obtaining various nozzle back pressures as actuator output signals determined by said electric input signals.

6. In an electro-hydraulic actuator, a housing formed with a motor chamber and a discharge chamber, a diaphragm mounted between said chambers, a flow restrictor carried by said diaphragm, passages in said housing leading from said chambers and merging as a common discharge passage, an orifice in said common discharge passage, a nozzle arranged to discharge into said discharge chamber against said flow restrictor, a source of supply of high pressure fluid to said nozzle, an orifice between said source of supply and said nozzle, electric motor means mounted in said motor chamber and operatively connected with said flow restrictor for restricting flow from said nozzle in response to electric input signals applied to said motor means thereby obtaining respective nozzle back pressures as actuator output signals.

7. In an electro-hydraulic actuator, a housing formed with a motor chamber and a discharge chamber, a diaphragm assembly mounted between said chambers and including a flow restrictor, passages in said housing leading from said chambers and merging as a common discharge passage, an orifice in said common discharge passage, a nozzle arranged to discharge into said discharge chamber against said flow restrictor, electromagnetic motor means mounted in said motor chamber for selectively applying various input forces in response to electric input signals, and means for transferring said input forces through said diaphragm assembly to said flow restrictor for respectively restricting the flow from said nozzle thereby obtaining various nozzle back pressures as actuator output signals determined by said electric input signals.

References Cited in the file of this patent UNITED STATES PATENTS 1,611,961 Thompson Dec. 28, 1926 1,973,769 Lehn Sept. 18, 1934 1,992,048 Temple Feb. 19, 1935 2,584,455 Hughes Feb. 5, 1952 2,601,867 Alyea July 1, 1952 2,742,916 Side Apr. 24, 1956 

